Cleaning of CHF₃ plasma-etched SiO₂/SiN/Cu via structures using a hydrogen plasma, an oxygen plasma, and hexafluoroacetylacetone vapors

Cleaning processes for CHF₃ reactive ion etched Cu vias, consisting of exposure to a hydrogen plasma, an oxygen plasma, and hexafluoroacetylacetone [H(hfac)] vapors have been investigated. After each step in the cleaning process, the dielectric surface and the Cu surface of via structures were analyzed by in situ by angle-resolved x-ray photoelectron spectroscopy. A hydrogen plasma was effective in removing carbon and fluorine deposits on all of the surfaces, and CuO and Cu₂O on the Cu surface at the via bottom. It was not effective, however, in removing the Cu deposited on the dielectric surfaces. An oxygen plasma is effective in removing all the carbon and some fluorine deposits. Cu deposits on the dielectric surfaces were not removed, however, and the Cu surface was oxidized. Exposure to H(hfac) vapors reduced some of the Cu deposits on the dielectric, however Cu diffusion into SiO₂ possibly occurred during this exposure at the elevated temperature of 200 °C. CuO and Cu₂O were removed by the H(hfac) exposure above 150 °C. A three-step cleaning sequence was devised which consists of a brief oxygen-plasma exposure, a dilute-HF solution dip, followed by exposure to H(hfac) vapors. The cleaning sequence is effective in obtaining a clean dielectric surface and an oxide-free Cu surface at the via bottom that allows low contact resistances of 5.8-6.8×10^-11 Ω cm².